Slush freezing apparatus as shown, for example, in U.S. Pat. Nos. 3,698,203; 3,180,110 and 3,069,866, is subject to the problem of formation of ice in the upper liquid reservoir, either because of ice which forms on the upper surface of the chilled divider plate or which migrates upwardly through passage means which provides for flow of liquid from the reservoir to the freezing chamber. Formation of such ice may block flow of liquid from the reservoir to the freezing chamber and render the apparatus inoperative.